The present invention relates to a semiconductor integrated circuit for communication having a PLL (Phase-Locked Loop) circuit built therein, which generates a carrier wave signal supplied to a demodulator for demodulating an RF receive signal and a modulator for modulating a transmit signal, and a technique for selecting a frequency band of a loop for the PLL circuit. The present invention relates to, for example, a technique effective if applied to a semiconductor integrated circuit for communication mounted in a wireless communication apparatus like a cellular phone having a mode for modulating only a phase component and a mode for modulating a phase component and an amplitude component.
In a wireless communication system like a cellular phone, a semiconductor integrated circuit for communication (hereinafter called high-frequency or RF IC) has been used in which a receive signal or a transmit signal is combined with an RF local oscillation signal (carrier wave signal) by mixers to perform frequency downconvert or upconvert, and modulation for the transmit signal and demodulation for the receive signal are performed. In such an RF IC, a technique is used wherein a carrier wave signal combined with the receive signal and a carrier wave signal combined with the transmit signal are generated by a common PLL circuit and supplied to a mixer on the receiving side and a mixer on the transmitting side to thereby achieve a reduction in chip size.
In a wireless communication system of a recent GSM (Global System for Mobile Communication) or the like, a system is being put to practical use, which includes a mode called an EDGE (Enhanced Data Rates for GSM Evolution) having a 3π/8rotating8-PSK (Phase Shift Keying) modulation mode for modulating a phase component and an amplitude component of a carrier wave in addition to a GMSK (Gaussian filtered Minimum Shift Keying) modulation mode for modulating the phase component of the carrier wave, and wherein the modulation modes are switched to perform communications. Since the amplitude modulation is performed in the EDGE mode in addition to the phase modulation, data communications faster than the GMSK mode at the phase modulation alone can be carried out.
In the wireless communication system of the GSM system, a TDM (Time Division Multiple Access) system has been adopted as a multiplexing system. Transmit and receive data are managed in the form of a unit called a frame comprised of 8 time slots (hereinafter called simply slots). Allocating data of one user to, for example, one slot makes it possible to allow eight users to share one channel (frequency) at maximum.
In an EDGE system, a technique called dynamic link adaptation has been adopted which performs switching between data coding (coding/combining) processing and a modulation system according to the distance between a terminal device and a base station. When, for example, the distance to the base station increases, I and Q signals of a baseband are given data coding processing low in data rate but resistant to noise and then subjected to GMSK modulation. When the distance to the base station is short, the I and Q signals are given data coding processing susceptible to noise but high in data rate and then subjected to 8PSK modulation.
Further, in the GSM system, there has been proposed a function called DTM (Dual Transfer Mode) which inserts data modulated in a GMSK mode and data modulated in an EDGE mode into the same frame and performs communications as shown in FIG. 11. Cellular phones each having such a function are expected to increase from now on. Incidentally, “MNT” in FIG. 11 indicates a monitor processing period in which the distance between a terminal device and a base station is measured. The GSM system has been disclosed in a patent document 1 (Japanese Unexamined Patent Publication No. Hei 11(1999)-168405).